Sonic well pump tubing string



July 18, 1961 A. G. BODINE 2,992,613

soNIc WELL PUMP TUBING STRING Filed Aug. 30, 1960 5 Sheets-Sheet 1 Z0 @li INVENTOR. fer 50am/f BY @f/Z July 18, 1961 A. G. BOBINE soNIc WELL.PUMP TUBING STRING 3 Sheets-Sheet 2l Filed Aug. 30, 1960 July 18, 1961A. G. BoDlNE soNIc WELL PUMP TUBING STRING 3 Sheets-Sheet 3 Filed Aug.30. 1960 JNVENTOR. #[5567 6? Ba/ME BY .gbme fr 2,992,613 SONIC WELL PUMPTUBING STRING Albert G. Bodine, 13120 Moorpark St., Sherman Oaks, Calif.Filed Aug. 30, 1960, Ser. No. 52,806 2 Claims. (Cl. 103-1) Thisinvention relates generally to sonic deep well pumps of the generalIclass first disclosed in my issued Patent No. 2,444,912, and moreparticularly to tubing couplings for such pumps.

This application is a continuation-in-part of my application Serial No.627,457, led December l0, 1956, now abandoned.

A sonic pump such as here contemplated operates by virtue of acousticwaves, i.e., periodic elastic deformation waves of tension andcompression, transmitted down the pump tubing from a wave generator atground level to a succession of valves located at various depths withinthe tubing. 'The tubing employed is, of course, of elastic material, soas to transmit such waves, and is made up in usual lengths connected bycouplings. These couplings comprise sleeves or collars, internally taperthreaded at each end, to receive the taper threaded ends of the tubing.

As these couplings are conventionally made, there exist certainrelatively large and sharp changes or discontinuities in both axial andcircumferential unit stress within the coupling sleeve and tubing atcertain locations therein, and these have two adverse effects; first, achange or discontinuity in elastic wave transmission, causing verymaterial wave reflections and consequent loss of wave energytransmission; and second, early acoustic fatigue failure of the tubing,and sometimes of the coupling sleeve. With respect to tubing andcoupling failure, it must be understood that the coupling is subject tohigh frequency cyclic stress reversals or variations in the operation ofthe wave transmission pump, and should hence be constructed to be strongagainst such cyclic fatigue failure. However, as actually constructed,the last or outside thread engaged is in a region where the conventionalcoupling sleeve has relatively great wall thickness, causing highcircumferential compressive stress and high radial shear in the tubing,which stress drops to Zero just `in back of this last thread. Axial unitstress also changes precipitously in both the tubing and coupling sleevein the region of the last thread engaged. This combination of sharpstress discontinuity creates a weakness at which fatigue failure islikely to occur under the condition of acoustic wave transmission. It isalso the sharp stress discontinuity in the region 'of this last threadengaged that is responsible for the very harmful acoustic wavereflection propensity mentioned above.

One object of the invention is accordingly the provision of a tubingcoupling for sonic wave transmission which materially reduces or avoidssharp stress changes or reliective discontinuities along the elasticwave path through the coupling, and a further object is the provision ofa tubing coupling for a sonic well tubing whose elastic modulus does notdepart, either sharply at any given point in the elastic wave path, orto any material extent, from the modulus of elastic tubing itself.

A still further object is the provision of a coupling for a sonic welltubing which avoids imposition of high compressive stress and radialshear in the tubing at the point of the last thread engaged, and whichthereby avoids a weakness point for acoustic fatigue failure.

The invention may best be understood in connection with the accompanyingdrawings, to which reference is made in the ensuing detaileddescription, and in which drawings:

States Patent nice FIG. l is a diagram of a conventional tubing couplingtogether with certain stress and load curves;

FIG. 2 shows a similar diagram and curves of the tubing coupling of theinvention;

FIG. 3 is a longitudinal sectional View through a preferred embodimentof coupling according to the invention;

FIG. 4 is a longitudinal sectional view of sonic pump tubingincorporating a sonic tubing string and tubing coupling in accordancewith the invention; and

FIG. 5 is an enlarged fragmentary section taken from FIG. 4.

In FIG. l is shown one-half of a conventional tubing coupling 10, and anend portion of a conventional upsetend tubing 11 screwed thereinto, withaccompanying circumferential and axial stress and load diagrams. Thetubing 1 1 has cylindrical side wall 12, enlarged or upset end portion13, and conventional exterior taper threads 14. Coupling 10 comprises asleeve having corresponding internal taper threads 15, and a threadrelief 16 at the end. The last thread engaged is indicated at 17.

It will be understood that the members are screwed tightly together, andthat the taper threads elastically expand the coupling sleeve to anextent, while the threaded end portion of the tubing is elasticallycompressed to an extent. The relative extents of such elasticdeformations depend upon the relative wall thickness at different crosssections along the joint. The resulting circumferential tension in theparticular coupling sleeve shown for points therealong is represented bycurve 20, and the resulting circumferential compression in the tubing isrepresented by Icurve 21. Owing to the substantial wall thickness ofcoupling 10 at the last thread engaged 17, the compression in the tubingis high at that point, and drops sharply to zero just outside thisthread, as shown at 22. The two curves 20 and 21 have broad tops ofopposite slopes owing to the reverse tapers, and the particular point tobe observed is that the stress in the tubing is at a near maximum atlast thread 17, and then drops sharply to zero, as earlier mentioned. Itis within the region of this sharp stress drop-olf, from near maximum tozero, that the tubing is most prone to cause elastic wave reflections,and also to give way in sonic pumping service by acoustic fatiguefailure.

The total axial loads in the tubing and coupling sleeve are representedby curves 30 and 31, respectively. Because of the substantial thicknessof the coupling sleeve out to the last thread 17 engaged with thetubing, this sleeve is elastically quite stiff, and most of the loadingis transferred from the tubing to the coupling sleeve within the lastfew threads of the latter. The load curves 30 and 31 thus drop sharplyfrom full load to zero within the length of these last few threads,crossing one another as shown. Curves 32 and '33, representing the unitaxial elastic stresses in the tubing and coupling sleeve, respectively,similarly drop sharply, within the length of the last few threads, froma high value to zero, also crossing one another, as shown. The drop 34in curve '32 results from the thick unthreaded section 13, and the riseat 35 results from the taper between the upset end and the thinner wall12. The slope of the top part of the cur've 33 is owing to the taper ofthe coupling sleeve.

These curves thus show that a sharp discontinuity of circumferentialcompression, from maximum to zero, at the last thread engaged with thecoupling; also, that axial stress in both the coupling sleeve and thetubing drops lfrom a high value to zero within the length of a very fewthreads from the last thread engaged.

The high compressional stress in the tubing at lastA4 17, followedimmediately by zero compressional thread the tubing is: subjected tostress just beyond said thread, means also that the tubing is subjectedto a high shear stress at thread 17, followed immediately by completerelief of this shear stress. T he shear stress curve, in fact, is of aform similar to the curve 20.

The total stress in the tubing at any point is the resultant ofcomponents of compressional, shear, and axial stresses, and it will beseen from the curves that the resultant of these stresses is maximizedin the region of the last thread 17, while all these stresses fall tozero within a very short distance. This creates a weakness in the regionof the tubing at the last thread engaged, which may result in earlyfailure by acoustic fatigue under the cyclic axial stress changescontinuously imposed during operation of the pump.

Of even greater moment is the fact that the sharp stress discontinuitiesdescribed, both circumferential, as represented by the leg 22 of curve21, and axial, as represented by the steep, crossing portions of curves32 and 33, create steep, sharp changes in acoustic wave transmissionproperties When the tubing is in service in a sonic pump installation.Very material wave retiections occur at these discontinuities, withcorresponding loss in wave energy transmission. At each suc-h sharpstress discontinuity in the acoustic wave path down the pump tubing, aloss in wave energy is suffered. In another manner of speaking, the wavedecrement at each tubing coupling is quite large, and under suchconditions, insufcient wave energy can be transmitted down a sonic pumptubing for good pumping action in the lower regions of a deep sonicpump. This condition prevails before the tubing fails by acousticfatigue, as explained above, and prevails even if the tubing in a giveninstallation does not suffer failure by such fatigue. Of course, for anygiven installation, with any specific design of tubing coupling, theacoustic waves sent down the tubing can be held to a safe amplitude, atwhich long tubing life can be predicted. This is one solution for theproblem of tubing failure, though, of course, not a desirable one, sinceit means limitation of power, and a consequent limitation on productionvolume. No similar solution is available, however, for the problem ofwave decrement (reflection losses at each coupling), since each couplingimposing a change in stress concentration acts to choke the flow ofavailable acoustic wave energy down the tubing. Thus, even though thesonic pump be operated under conditions such that tubing failure is nolonger a hazard, yfractional Wave energy loss at each coupling is stillpresent.

FIG. 2 is a diagram similar to that of FIG. l, but showing the improvedcoupling of the present invention, and the improved stress distributiongained thereby. The improved coupling sleeve is indicated at a (see alsoFIG. 3, showing a longitudinal section of the complete coupling of theinvention), and at 11a is indicated the end portion of a conventionalupset-end tubing, like that shown in FIG. l. Portions of tubing 11acorresponding to tubing 11 are indicated by the same reference numerals,but with addition of the suix a.

Coupling sleeve 11a has as its essential modification a substantialexterior taper, such as indicated at 40, typically of the order of10-12, along its taper threaded region. It also preferably has a centralthread relief, as at 4l. Beyond its last thread 17a, at the end of thetaper 40, it Ipreferably has a faired or streamlined ilare 42terminating in an enlarged ring section or annulus 43, whose insidediameter is substantially greater than the major diameter of the lastthread 17a, and whose outside diameter may be equal to the maximumoutside diameter of the coupling sleeve. This annulus functions as areinforcement of the coupling during handling and during the occurrenceof lateral vibrations incident to the elastic wave transmission, andserves also as a funnel mouth to facilitate entering the tubing andthereinto during coupling. It will be readily apparent that the taper 40progressively reduces the elastic stiffness of the coupling sleevetoward its ends, yboth circumferentially and axially,

both of which reductions in stiffness contribute important improvementsin stress distribution and in elastic wave transmission properties.

Curve 21a is the new curve of circumferential stress distribution in thetubing. Since the tapered coupling sleeve is progressively less stii,circumferentially, in the direction toward the last thread 17a, thecompression which i-t imposes on the tubing is progressively reduced,and instead of a sharp drop-off, as at 22 in FIG. l, the falhoff portion22a of compression distribution curve 21a tapers from maximum to zeroover substantially the full length of the engaged threads between thecoupling and tubing. There is thus no stress concentration in the tubingat last lthread 17a, and no sharp and large reduction in compressivestress 'and shear in the tubing.

Axial load and unit stress distribution are also made materially moregradual as a consequence of the taper of the coupling, and the resultingprogressively diminishing elastic stiffness in the axial direction.Because the coupling is materially less stiff, axially, in its endregion, the last few threads engaged no longer monopolize the load.Instead, the end region of the coupling is capable of increasedlongitudinal elastic elongation and contraction under axial loadingcycles of wave transmission, and such capability for elastic elongationis progressively increased from the center towards the ends, i.e.,towards and to the last thread 17a. As a consequence of this increasedand controlled capability for longitudinal elastic deformation, the loadtransference between the threads of the tubing and coupling occurssubstantially throughout the engaged threads therebetween. This isrepresented by the axial load curves 30a and 31a of FIG. 2, and theextension of the length of the thread region throughout which the loadtransference occurs will be apparent from a comparison of curves 30a and31a of FIG. 2 with curves 30 and 31 of FIG. l.

The corresponding axial uni-t stress distribution curves 32a and 33a forthe tubing and coupling sleeve reveal that the unit axial stress in eachnow falls from maximum to zero over a much longer length of the engagedthreads. Instead of the large and sudden axial stress fall-off, as shownby curves 32 and 33 of FIG. 2, there has been achieved the gently andgradually falling stress decrease curves 32a and 33a of FIG. 2.

FIGS. 4 and 5 show a typical example of the sonic pump combination whichembodies the coupling described above. This pump operates by vibratoryimpulses applied to uid impelling and check valve element ISa mounted inthe tubing string 11a. These vibratory impulses are accomplished bytransmitting sonic elastic vibration waves down the tubing string 11a,so that regions of the tubing are caused to elongate and contract in avibratoryV manner. The iluid impelling and check valve means 15a arelocated in the vibratory regions of the tubing string. In this mannerfluid is pumped along the tubing string. Said pump is fully described inmy Patent Number 2,7 02,- 559.

I have found that the couplings described above are very effectivetransmitters of the sonic waves. These couplings do not reflect thesound waves, but rather transmit the waves on through efliciently, whichis important for long transmission in deep wells.

Two different but related benefits are to be observed. The first ofthes'e is the relief of the major part of the compressive stress in thetubing in the region of the last thread engaged, with consequent virtualelimination of the Weakness region at that point as regards elasticfatigue from acoustic vibrations. In this connection, the total stressin the tubing at this point is again the resultant of the axial stresscomponent, which is substantially unchanged, and the compressive stressand shear, which are now reduced to a small fraction of their value whenusing a conventional coupling. The coupled tubing is thus relieved ofthe hazard of early acoustic fatigue failure when used in sonic pumpingservice.

The second and more profound improvement is that, in consequence of thecircumferential stress in the tubing, and the axial stress in bothtubing and coupling sleeve, all undergoing changes from maximum tominimum over long lengths of the engaged threads, instead of entirelywithin the region of the last thread engaged, there have been achievedlong, gradual stress' transitions, which are not prone to wavereflections. In a manner of speaking, there has been provided astreamlined wave transmission path through the coupling. Acoustic wavedecrement at each coupling is very greatly reduced. Acoustic wave energyows smoothly and uninterruptedly down the tubing, without suiering amaterial fractional loss at each coupling. Materially greater sonicenergy can accordingly be transmitted to the lower regions of the sonicpump tubing for any given force impulse at the upper end. Put in stillother language, the longitudinal elastic modulus of the coupling hasbeen made to approach closely that of the tubing wall. The final effectis improved eiciency, and improved pumping action within the lowerregions of the sonic pump by reason of greater energy delivery thereto.The improved coupling will be seen, therefore, to be of improvedstrength against acoustic fatigue, and therefore to permit use of higheramplitude wave energy, and also to transmit a materially largerproportion of the acoustic wave energy transmitted thereto, giving bothimproved eiciency, and a materially higher available wave energy level,particularly in the lower regions of a deep sonic Well pump.

I claim:

1. A deep Well pump which includes: an oscillatory uid impelling pumpingmember adapted for placement in the well, a sonic wave generator locatedat the ground surface, and an elastic pump tubing string operativelyinterconnecting said sonic wave generator and said oscillatory duidimpelling pumping member, said elastic tubing string being adapted totransmit elastic deformation waves of compression and tensionlongitudinally therethrough from said generator to said pumping member,said tubing string comprising at least two lengths of elastic tubinghaving taper threaded ends, and a coupling sleeve joining adjacent endsof said tubing lengths, the two opposite end portions of said sleevebeing internally divergent toward the extremities thereof and taperthreaded for reception of the taper threaded end of the tubing lengths,and having also external wall surfaces converging progressively at asubstantial angle toward the eX- tremities thereof to points oppositethe outermost threads thereof engaged with the threaded ends of thetubing lengths, and to a thickness at said points materially less thanthe wall thickness of the tubing ends opposite said last threadsengaged, all in such manner as to attain long, gradual uniformlyprogressive stress transitions in the threadedlfy engaged sleeve andtubing ends, whereby to minimize coupling reflections of elasticdeformation waves transmitted along the tubing string and to attain lowdecrement wave transmission therealong.

2. The subject matter of claim l, wherein the tapered portions of thecoupling sleeve merge, outside said points opposite the outermostthreads engaged, with flaring wall portions terminating in end collarsof substantial thickness whose inside diameter is greater than themaximum major diameter of the taper threads on said sleeve and tubingends.

References Cited in the le of this patent UNITED STATES PATENTS 263,943Morse Sept. 5, 1882 1,265,418 Baldwin May 7, 1918 2,205,697 ScharpenbergJune 25, 1940 2,261,566 Russell Nov. 4, 1941 2,418,418 Martin Apr. 1,1947 2,440,651 Bell Apr. 27, 1948 2,553,542 Bodine May 22, 1951 FOREIGNPATENTS 464,847 Italy July 23, 1951

